In the broadcast industry, certain devices such as television cameras, particularly high performance cameras used in program production, can be remotely controlled and powered from a local or distant camera control unit (CCU), sometimes called a base station. There are two prominent types of transmission mediums (i.e., cables) in the industry for carrying signals between the CCU and the camera. One type is a triaxial cable and the other is an fiber optic/electrical hybrid cable. Both of these cable types are used to power the camera and transmit video, audio, and data signals from and to the camera.
Triaxial cables and triaxial connectors are the more traditional media used in the industry. A triaxial cable and corresponding connector consists of three conductors. The triaxial structure is a coaxial design with an extra conductive shield. On a triaxial structure, the center pin carries all signals from and to the camera. These signals vary with the camera type and sophistication. For example, the signals coming from the camera may include, but are not limited to, video, intercom, and audio. The signals going to the camera may include, but are not limited to, program audio, intercom, teleprompter feed, and data for controls. These signals may be analog, such as AM or FM, and/or digital in nature.
The signals are typically carried simultaneously bi-directionally between the CCU and the camera. Since there is typically only one physical cable, it is the function of the triaxial adapter of the camera system to encode and/or modulate the required video, audio, intercommunications, and data signals onto the proper frequencies. The different signals are demodulated to allow them to be carried on the center pin in both directions. The different frequencies are specified by the camera manufacturers.
The center pin also carries the power from the CCU to the camera. The middle shield of the triaxial cable is used as the power shield. The outer conductor is used as a protection shield. Camera voltage varies from one manufacturer to another and from one model to another. The most common voltages used in the industry are 250 Volts AC and 140 Volts DC. The power needed to power the camera, however, is normally no more than 10–17 Volts DC.
The triaxial structure is a robust structure. The triaxial camera connectors and cables are large and capable of being used in harsh environments, such as at sporting events. The triaxial structure has been in the market for a long time due to its ruggedized structure. Many improvements have been made to the triaxial connectors over the years. There are several major triaxial connector interfaces in the world terminating the same type of a triaxial cable. U.S. Pat. Nos. 6,575,786 and 5,967,852 show triaxial connectors including the end structures to connect to mating triaxial connectors.
However, the triaxial structure has its drawbacks. The operating distance of existing triaxial systems is limited. For example, a high definition (HD) signal can be transmitted over a triaxial structure for a maximum of only about 2500 ft. Since the trend in the industry has been toward cameras having higher performance and wider information bandwidths, other solutions are being explored.
The second type of a transmission medium, designed to compensate for the limitations of the triaxial cable, is an electrical/fiber optic hybrid medium. There are several hybrid camera connectors available in the industry for terminating a hybrid cable. Many use the SMPTE 311M standard. The type of signal needed remains the same as for the triaxial system. Typically, the hybrid SMPTE cable carries two fiber signals, one for transmitting and one for receiving, two copper signals for intercom, and two copper signals for power.
The hybrid cable has been favored for HD applications. It allows the signal to be carried over longer distances than on the triaxial cable structure. Generally, signals can travel further over fiber optic cables compared to copper cables. However, the hybrid system is not without its drawbacks also. The hybrid connectors that are used to terminate the hybrid cable are expensive and are not designed for harsh environments, making them often unreliable. Moreover, since the traditional triaxial structure has been adopted as the main camera standard in the broadcast industry, there are significant costs involved with investing in new cameras, CCU's and supporting infrastructure to accommodate hybrid connectors.
One solution provided in the industry has been to combine the advantages of the two types of cabling systems. FIG. 1 shows a prior art arrangement 10 that uses both a triaxial medium and an electrical/fiber optic hybrid medium between the camera and the CCU.
Referring to FIG. 1, in addition to a camera 12 and a CCU 14, the prior art camera system 10 generally includes a camera control interface unit 16, a camera interface unit 18, and a fiber optic cable 20. Control interface unit 16 is linked to CCU 14 using a triaxial cable 22. Similarly, camera interface unit 18 is linked to camera 12 using a triaxial cable 24. Control interface unit 16 and camera interface unit 18 each provide an electro/optical and opto/electrical conversion function. Control interface unit 16 converts electrical signals received from CCU 14 on triaxial cable 22 to provide an optical signal on fiber optic cable 20. The optical signal is transmitted on fiber-optic cable 20 to camera interface unit 18 where it is converted back to an electrical signal and passed to camera 12 on triaxial cable 24. In a similar manner, camera interface unit 18 converts the electrical signal received from camera 12 on triaxial cable 24 to provide an optical signal which is transmitted on fiber optic cable 20 to control interface unit 16. Control interface unit 16 converts the optical signal back to an electrical signal for transmission to CCU 14 on triaxial cable 22. Example camera interface units and/or control interface units such as herein described are available from Telecast Fiber Systems, Inc.
A system such as system 10 illustrated in FIG. 1 is complicated and costly. In addition to the camera 12 and the CCU 14, the system requires a control interface unit 16, a camera interface unit 18, and a total of twelve different connectors (eight triaxial and four fiber optic or hybrid connectors) to provide the connections. The connectors include one triaxial connector 26 located on the CCU 14, two triaxial connectors 28, 30 terminated to the ends of the triaxial cable 22 extending between the control interface unit 16 and the CCU 14, one triaxial connector 32 located on the control interface unit 16, one fiber optic or hybrid connector 34 located on the other side of the control interface unit 16, two fiber optic or hybrid connectors 36, 38 terminated to the ends of the fiber optic or hybrid cable 20 extending between the control interface unit 16 and the camera interface unit 18, one fiber optic or hybrid connector 40 located on the camera interface unit 18, one triaxial connector 42 located on the other side of the camera interface unit 18, two triaxial connectors 44, 46 terminated to the ends of the triaxial cable 24 extending between the camera interface unit 18 and the camera 12, and one triaxial connector 48 located on the camera 12. An example of a fiber optic/electrical connector such as the one in the prior art system of FIG. 1 is available from LEMO USA, Inc.
What is needed is a system that uses the more durable, traditional triaxial interface while allowing the signal to be carried over distances achievable only by fiber media. What is needed in the industry is a solution that enhances the operating distance of existing and new triaxial camera systems without having to modify existing camera and CCU hardware.